There is a growing need in the medical imaging sciences to better detect and characterize abnormal tissue and disease processes. Optical imaging in the near-infrared spectrum offers the possibility to employ fluorescently tagged reporter probes to obtain specific molecular information about a particular disease state. VisEn Medical, Inc. is pioneering the development of a novel optical molecular imaging technology platform that enables imaging of molecular activity in-vivo. This proprietary technology platform is based on near-infrared activatible optical probes that become activated only when they come in contact with the specific enzymes that they are designed to target. VisEn is currently developing a Cathepsin B enzyme-imaging probe for early clinical cancer detection. We have chosen to target the enzyme Cathepsin B as it is known to be associated with several different types of cancer, including colon and ovarian cancer, as well as other diseases such as arthritis and cardiovascular disease. The overall goal of this SBIR grant proposal is to test and characterize the different near infrared fluorochrome probes developed during Phase I of this project in different in-vivo disease models in order to select a candidate for clinical trials. The Specific Aims of this Phase II proposal are summarized below. 1. Test at least three different Cathepsin B probes in animal tumor models for their ability to detect cancer. 2. Evaluate the probes for their ability to detect different types of tumors, specifically colorectal and ovarian tumors. 3. Determine key preclinical Cathepsin B probe properties, including the pharmacokinetics, biodistribution and toxicity of the probes. 4. Conduct preliminary formulation and stability studies.